1. Field of the Invention
The present invention relates to a thin magnetic head provided with a magnetoresistive element.
2. Description of the Related Art
Conventional thin film magnetic heads provided with a magnetoresistive element (MR element) known in the art include an anisotropic magnetoresistive head (AMR head) making use of-anisotropic magnetoresistive effect and a giant megnetoresistive (GMR) head making use of spin-dependent scattering of conduction electrons. A spin-valve magnetic head that exhibits a high magnetoresistive effect in a low external magnetic field is disclosed in the specification of U.S. Pat. No. 5,159,513 as one embodiment of the GMR head.
FIG. 23 illustrates the construction of the conventional AMR head. The conventional AMR head comprises a lower gap layer 8 formed on a lower shield layer 7 comprising a magnetic alloy such as Sendust (a Fexe2x80x94Alxe2x80x94Si alloy). An AMR element layer 10 is laminated on this lower gap layer 8. This AMR element layer 10 is formed by depositing a non-magnetic layer 12 on a soft magnetic layer 11 followed by depositing a ferromagnetic layer (AMR feedstock layer) 13 on the non-magnetic layer 12. Magnetic layers 15 are provided at both sides of the AMR element layer 10, and conductive layers 16 are additionally provided on the magnetic layer 10.
An upper gap layer 18 is further formed on the conductive layers 16 and AMR element layer 10, and an upper shield layer 19 is further formed on the upper gap layer 18.
The ferromagnetic layer 13 that exhibits the AMR effect has been regarded to require two bias electric fields for optimum operation of this sort of the AMR head.
The first bias magnetic field is applied along the direction perpendicular to one face of a magnetic medium (the Z-direction in FIG. 23) and parallel to the face of the ferromagnetic layer 13, in order to allow resistance changes of the ferromagnetic layer 13 to linearly respond against the magnetic flux from the magnetic medium. This first bias magnetic field is usually termed a transverse bias, which allows the soft magnetic layer 11 to be magnetized along the Z-direction by a magnetic field generated by flowing a sensing current from the conductive layer 16 to the AMR element layer 10. Magnetization of the soft magnetic layer 11 endows the ferromagnetic layer 13 with a transverse bias along the Z-direction.
The second bias magnetic field is usually termed a vertical bias, which is applied parallel to the magnetic medium and film face of the ferromagnetic layer 13 (the X-direction in FIG. 1). The vertical bias magnetic field is applied in order to suppress Barkhausen noises generated by forming a number of magnetic domains in the ferromagnetic layer 13 or, in other words, to obtain a smooth resistance change with few noises against the magnetic flux from the magnetic medium.
The ferromagnetic layer 13 should be made to be a single magnetic domain for suppressing the Barkhausen noise described above. The vertical bias is usually applied by two methods for suppressing the Barkhausen noise. The first method comprise using a leak magnetic flux from the magnetic layer 15 by disposing two magnetic layers 15 and 15 at both sides of the ferromagnetic layer 13, while the second method comprises using an exchange anisotropic magnetic field generated at the contact-interface between an antiferromagnetic layer and ferromagnetic layer.
FIG. 24 shows the construction of a spin-valve type GMR head making use of the exchange anisotropic coupling of the antiferromagnetic layer.
The GMR head shown in FIG. 24 differs from the AMR head shown in FIG. 23 in that a GMR element layer 20 is provided instead of the AMR element layer 10.
The GMR element layer 20 is composed of a free ferromagnetic layer 22, non-magnetic intermediate layer 23, pinned ferromagnetic layer 24 and antiferromagnetic layer 25.
In accordance with the structure shown in FIG. 24, magnetization should be aligned toward the track direction while allowing the free ferromagnetic layer 22 to form a single magnetic domain by applying a bias along the track direction (X-direction in FIG. 24) using the magnetic layers 15 and 15, as well as aligning the magnetization of the pinned ferromagnetic layer 24 toward the Z-direction in FIG. 24, or along the Z-direction in FIG. 24 while allowing the pinned ferromagnetic layer 24 to form a single magnetic domain by applying a bias along the direction perpendicular to the magnetization of the free ferromagnetic layer 22. In other words, the direction of magnetization of the pinned ferromagnetic layer 24 should not be changed by the magnetic flux (Z-direction in FIG. 24). Rather, the linear response of the magnetoresistive effect is obtained by allowing the direction of the free ferromagnetic layer 22 to change within a rage of 90xc2x0 xc2x1xcex8xc2x0 relative to the direction of magnetization of the pinned ferromagnetic layer 24.
Relatively a large bias magnetic field is required for fixing the direction of magnetization of the pinned ferromagnetic layer 24 along the Z-direction. The larger the bias magnetic field is, the better pinning effect is obtained. At least 100 Oe of the bias magnetic field is required for surmounting the anti-magnetic field along the Z-direction in FIG. 24 and for preventing fluctuation of the direction of magnetic field due to the magnetic flux from the magnetic medium. The method for obtaining such bias magnetic field as described above comprises to take advantage of the exchange anisotropic magnetic field generated by providing the antiferromagnetic layer 25 in close contact to the pinned ferromagnetic layer 24.
In the structure as shown in FIG. 24, magnetization of the ferromagnetic layer 24 is fixed along the Z-direction by the exchange anisotropic coupling generated by providing the antiferromagnetic layer 25 in close contact to the pinned ferromagnetic layer 24. Therefore, the electric resistance of the GMR element layer 20 is changed by changing the direction of magnetization of the free ferromagnetic layer 22 when a leak magnetic field from the magnetic medium traveling along the Y-direction is applied, thus enabling the leak magnetic field from the magnetic medium to be sensed by this resistance change.
The bias magnetic field is applied to the free ferromagnetic layer 22 for the purposes of securing linear responses and suppressing the Barkhausen noise generated by forming many magnetic domains. The bias is applied by the same method as in the vertical vias in the AMR head or, in other words, the leak magnetic flux from the magnetic layer 15 is utilized as the bias by providing the magnetic layers 15 at both sides of the free ferromagnetic layer 22 in the construction as shown in FIG. 24.
It is known in the art that the temperature in the vicinity of the MR element layer such as the AMR element layer and GMR element layer is readily increased up to 120xc2x0 C. due to the heat caused by the stationary sensing current during operation of the thin film magnetic head. The MR element is so sensitive to temperature changes that electric resistance of the ferromagnetic layer is changed due to temperature increase of the MR element layer by the heat generated as described above, causing disturbance of read signals. Moreover, the exchange anisotropic magnetic field generated by the antiferromagnetic layer comprising FeMn and the like is also very sensitive to temperature changes in the GMR element, and the exchange anisotropic magnetic field nearly linearly decays -against the temperature before it is extinguished at about 150xc2x0 C. (blocking temperature: Tb). Therefore, a stable exchange anisotropic magnetic field can not be obtained due to the problems as described above.
The conventional thin film magnetic head for solving the problems as hitherto described comprises upper and lower gap layers 8 and 18 made of alumina (Al2O3) in the AMR element layer 10 or GMR element layer 20. The generated heat is dissipated by slowly transferring it to the shield layers 7 and 19 through the gap layers 8 and 18.
In order to comply with ever growing recent requirements for further improving output levels of the thin film magnetic head, the stationary sensing current density flowing through the MR element layer should be increased by, for example, reducing the thickness or diminishing the length of the MR element.
However, the heat generated by the stationary sensing current cannot be sufficiently dissipated through the gap layers 8 and 18 made of alumina, when the stationary sensing current density is increased in the conventional thin film magnetic head. Consequently, defects and cracks are caused in the MR element layer, or elements are diffused among the layers constituting the MR element layer to disturb compositions of the component materials in each layer, thereby deteriorating linear responses or decreasing the suppressing effect for the Barkhausen noise. Accordingly, it was difficult to improve the output level by merely making the MR element small size or improving the current density by increasing the stationary sensing current.
Accordingly, the object of the present invention is to provide a thin film magnetic head having good linear responses and suppressed Barkhausen noises, wherein the MR element layer is prevented from heat diffusion and baking loss due to temperature increase by allowing the heat generated by the stationary sensing current to be effectively dissipated to suppress decrease of output levels and deterioration of the exchange anisotropic magnetic field.
With respect to the materials to be used for the gap layers, it was presumed that the heat generated by the stationary sensing current could be efficiently dissipated by using aluminum nitride (AlN) having good heat conductivity in place of alumina that has been conventionally used.
However, since a photolithographic process comprising coating of a resist, exposing to light, development with a strong alkaline solution and rinsing with water is required for forming the MR head, a short-circuit of the flowing sensing current may occur when the gap layer is composed of an aluminum nitride film, because aluminum nitride is very soluble in the strong alkaline solution. Further, aluminum nitride readily reacts with water to form a water-soluble compound. Therefore, reliability of the MR head is compromised because the aluminum nitride film is dissolved in the rinse process for forming the MR head, or by absorbing moisture in the air even after the MR head has been formed.
Otherwise, since the aluminum nitride film has a large film stress, the film is liable to be pealed off during or after forming the MR head to leave some problems in reliability.
For solving these and other problems as described above, elements X selected from Si, B, Ge and C that readily react with N and have good resistivity against a strong alkaline solution and water was added to an insulation layer containing Al and N, as well as O that readily react with the elements X, to obtain a highly heat-conductive insulation layer containing Al, N, X and O, thereby constructing a gap layer comprising the highly heat-conductive insulation layer. Otherwise, the object of the present invention can be attained by forming a highly heat-conductive insulation layer containing Al, N, X and O in the gap layer in order to endow the gap layer with a better heat conductivity than alumina, much smaller solubility in the strong alkaline solution and water as compared with the film comprising aluminum nitride, and having small film stress.
For solving the foregoing problems, there is provided in accordance with one aspect of the present invention a thin film magnetic head comprising at least a layer of a magnetoresistive element formed on a lower shield layer via a lower gap layer, electrode layers for imparting a sensing current to the magnetoresistive element, and an upper shield layer formed on the electrode layer via an upper gap layer, wherein at least one of the lower gap layer and upper gap layer has a highly heat-conductive insulation layer containing at least Al, N, X and O, the element X being at least one element selected from Si, B, Ge and C.
The construction of the thin film magnetic head in accordance with the present invention allows the heat generated by the stationary sensing current to be efficiently dissipated. Therefore, output levels of the magnetic head are improved and a sufficient intensity of the exchange anisotropic magnetic field required for the thin film can be applied while obtaining a resistance change excellent in linear response without causing any Barkhausen noise, thereby enabling excellent read performance to be obtained. The gap layer comprising a highly heat-conductive insulation layer containing at least Al, N, X and O has a good resistivity against the strong alkaline solution and water. Small film stress can prevent the film from being peeled off during or after forming the MR head to provide a reliable product.
It is preferable for improving heat conductivity and resistance against the strong alkaline solution and water in the thin film magnetic film according to the present invention that the highly heat-conductive insulation layer is composed of a texture comprising fine crystals comprising fine crystalline AlN grains and a crystal containing at least two elements comprising the elements X, N and O, or a texture comprising a mixed phase of a fine crystalline phase comprising the fine crystalline AlN grains and an amorphous phase containing at least two elements X, N and O.
It is also preferable for improving heat conductivity and resistance against the strong alkaline solution and water in the thin film magnetic film according to the present invention that the element X in the highly heat-conductive insulation layer is chemically bound to at least one of the elements O and N.
Also, it is preferable for improving heat conductivity and resistance against the strong alkaline solution and water of the gap phase, and for reducing the film stress in the thin film magnetic film according to the present invention that the highly heat-conductive insulation layer contains the elements X and O in with a composition ratio within the range of more than zero atomic percentages and less than 20 atomic percentages, respectively.